1. Field of the Invention
This invention relates to a recording medium. This invention particularly relates to a recording medium provided with a recording layer comprising a material, which has properties such that, when light having a predetermined wavelength is irradiated to the material, the material is capable of being caused to change into a fluorescent material. This invention also relates to a method and apparatus for recording information, in which the recording medium is utilized. This invention further relates to a method and apparatus for reproducing information, in which the recording medium is utilized.
2. Description of the Related Art
There have heretofore been proposed various recording media, each of which is provided with a recording layer having properties such that, when light, such as a laser beam having been converged into a small beam diameter, is irradiated to the recording layer, a change in characteristics is caused to occur at a local area limited site of a material constituting the recording layer. By the utilization of the properties of the recording layers of the recording media, information, such as image information or computer data, is capable of being recorded on the recording media. As the recording media described above, recording media, such as CD-R disks, wherein only one piece of information is capable of being recorded at a single point on the recording layer, were popular in the past. Recently, recording media enabling multiple recording, wherein multiple pieces of information are capable of being recorded at a single point on the recording layer and the information is thus capable of being recorded at a high density, have been proposed.
As the recording media described above, recording media provided with recording layers constituted of fluorescent materials have been proposed. With the conventional recording media of the types described above, ordinarily, recording and reproduction of information are performed by the utilization of the characteristics such that, when recording light is irradiated to the recording layer constituted of the fluorescent material and excitation light acting as reproducing light is then irradiated to the site on the recording layer, which site has been exposed to the recording light, the intensity of the fluorescence, which is produced from the site having been exposed to the recording light, becomes lower than the intensity of the fluorescence, which is produced from the site having not been exposed to the recording light, or the wavelength of the fluorescence, which is produced from the site having been exposed to the recording light, varies from the wavelength of the fluorescence, which is produced from the site having not been exposed to the recording light.
However, with the conventional techniques for performing the recording and the reproduction of the information in the manner described above, in cases where the excitation light is irradiated to the site having not been exposed to the recording light, as in cases where the excitation light is irradiated to the site having been exposed to the recording light, the fluorescence is produced from the site having not been exposed to the recording light, though the intensity or the wavelength of the fluorescence varies from the intensity or the wavelength of the fluorescence produced from the site having been exposed to the recording light. Therefore, the problems occur in that the fluorescence produced from the site having not been exposed to the recording light acts as a background, and a reproduced signal having a high signal-to-noise ratio cannot always be obtained.